EFFECTS OF (R)-ALPHA-METHYLHISTAMINE AND SCOPOLAMINE ON SPATIAL-LEARNING IN THE RAT ASSESSED USING A WATER MAZE

The effects of (R)-alpha-methylhistamine ((R)-alpha-MeHA, a selective H-3-receptor agonist) and scopolamine (SCOP, a muscarinic antagonist) were investigated on spatial learning and memory in the rat (Hooded Li ster) using a water maze (WM). (R)-alpha-MeHA treatment (6.3 and 10 mg /kg IP) had no apparent effect on spatial learning but did result in e nhanced spatial recall at the higher dose, assessed by a transfer (pro be) test after training. In contrast, SCOP (0.5 mg/kg IP) induced a le arning and memory deficit measured both during and after training. In animals treated with (R)-alpha-MeHA and SCOP, (R)-alpha-MeHA partially (6.3 mg/kg) and completely (10 mg/kg) reversed the SCOP-induced defic it during the training phase, while in the post-training transfer test , (R)-alpha-MeHA (10 mg/kg) significantly reduced the SCOP-induced mem ory deficit. None of the treatments described resulted in impaired vis ual acuity as demonstrated by a raised platform test. These results ar e consistent with a role for histamine in cognitive processes and sugg est a possible interaction between central histamine and cholinergic m echanisms associated with rodent spatial learning and memory.